Problem: Simplify the following expression: $k = \dfrac{3r^2 - 3qr}{6qr} - \dfrac{qr - 4pr}{6qr}$ You can assume $p,q,r \neq 0$.
Answer: Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{3r^2 - 3qr - (qr - 4pr)}{6qr}$ $k = \dfrac{3r^2 - 4qr + 4pr}{6qr}$ The numerator and denominator have a common factor of $r$, so we can simplify $k = \dfrac{3r - 4q + 4p}{6q}$